This invention relates to the field of electromedical devices, and more particularly relates to leads for use in conjunction with medical devices.
A wide variety of implantable medical devices such as cardiac pacemakers, cardioverters, defibrillators, neural stimulators, and the like, have been known and commercially available for many years. Often, such devices are used in conjunction with one or more leads, which serve to conduct electrical stimulating pulses from the device to a desired location in the body, for example, the atrium or ventricle of a patient's heart. A lead may also serve to conduct electrical signals, such as a patient's electrical cardiac signals, to the implanted device.
In the case of cardiac pacing leads, the lead is introduced into the patient through a small incision at or near the implant site. The distal end of the lead is first introduced into the patient's vein. Then, the implanting physician directs the distal end of the lead through the vein and into the heart. Once the lead is positioned, the proximal end is connected to the implantable pacemaker. A somewhat larger incision is then made at the implant site, allowing, the pacemaker to be inserted under the skin.
In order to facilitate the introduction of a lead into the patient, a stylet can be employed. A stylet is a relatively stiff wire-like element that may be used during the implantation procedure to give the lead increased rigidity. In order to use a stylet the lead must be designed to permit insertion of the stylet into a cylindrical bore, or lumen. The lumen may be defined by a coiled lead conductor or by a separate plastic tube. Both alternatives are illustrated in U.S. Pat. No. 3,348,548, issued to Chardack. Alternatively, a tubular plastic stylet guide may be located in the lumen of a coiled conductor, as illustrated in U.S. Pat. No. 4,944,088, issued to Doan et al.
Often, a physician will impart a curve to the stylet, for example at the stylet's distal end, so that after insertion of the stylet into the lead, the curvature of the stylet is imparted to the lead itself. The curvature of the stylet, and hence of the lead surrounding the stylet, can greatly facilitate the navigation of the lead through the venous system and to its desired location within the heart.